Title: Bio-control ability of Trichoderma species against spot blotch disease (wheat) causing pathogen Bipolaris sorokiniana under in vitro conditionAbstract:Spot blotch disease of wheat caused by Bipolaris sorokiniana (Shoem.) occurs every year in plain areas of Nepal causing considerable losses of grain yield. Several Trichoderma species possess antagonistic ability against different pathogens. In-vitro studies were conducted to explore the natural antagonistic aptitude of selected Trichoderma species against B. sorokiniana. Dual culture technique was followed to assess the antagonistic ability of five isolates of Trichoderma species against the pathogen. The experiment was conducted following Completely Randomized Design (CRD) with four replications. Radial growth of B. sorokiniana in dual culture with selected isolates of Trichoderma species was measured to compare the antagonistic ability of the selected Trichoderma species. Effects of interaction on viability of mycelium and on sporulation ability of the pathogen were assessed. Prominent antagonistic ability of Trichoderma species was identified from in-vitro dual culture studies. The evaluation of five isolates of Trichoderma species revealed that all the isolates significantly reduced the growth of B. sorokiniana in dual culture. Trichoderma sp. significantly inhibited the growth of B. sorokiniana by entirely covering the colony without completely killing the mycelia; however, the B. sorokiniana’s mycelia obtained from overlapped area of the isolates had significantly lower viability than the control. Trichoderma species also significantly reduced the sporulation ability of B. sorokiniana. The tested isolates of Trichoderma spp. had sturdy antagonistic ability against B. sorokiniana under in vitro condition. However, to exploit the isolates for bio-control of spot blotch disease under field conditions, further studies under in-vivo conditions must be needed.Key Words: Antagonist, Dual culture, Radial growth, Sporulation and Viability